DolphinQt: Reset TAS input slider to default on right-click

This is a feature which existed in DolphinWX. Seems like it got
implemented in DolphinQt for IRWidget/StickWidget but not sliders.

Source/Core/DolphinQt/TAS/TASSlider.cpp

@@ -0,0 +1,24 @@
+// Copyright 2020 Dolphin Emulator Project
+// Licensed under GPLv2+
+// Refer to the license.txt file included.
+
+#include "DolphinQt/TAS/TASSlider.h"
+
+#include <QMouseEvent>
+
+TASSlider::TASSlider(int default_, QWidget* parent) : QSlider(parent), m_default(default_)
+{
+}
+
+TASSlider::TASSlider(int default_, Qt::Orientation orientation, QWidget* parent)
+    : QSlider(orientation, parent), m_default(default_)
+{
+}
+
+void TASSlider::mouseReleaseEvent(QMouseEvent* event)
+{
+  if (event->button() == Qt::RightButton)
+    setValue(m_default);
+  else
+    QSlider::mouseReleaseEvent(event);
+}